This project will investigate the genetic, physiological and biochemical characteristics of a new class of mutants of Escherichia coli which exhibit an altered cell division pattern. The overall goal will be to use distortions apparent in the mutants to identify and study genes and proteins that regulate the division process. These studies will hopefully provide basic information with applications in higher organisms where mutations affecting regulation of cell division can lead to uncontrolled growth and tumor formation. The primary defect in the mutants is located in a previously unidentified gene, termed sfiD which lies near 64 minutes on the E. coli chromosome. The sfiD mutations prevent the action of two division inhibitors, SfiA and SfiC, whose synthesis is stimulated as part of the recA-dependent response to DNA damage. A second phenotype of the sfiD mutants is poor growth at low temperatures. Both SfiA and SfiC are known to inhibit ftsZ protein stabilities, FtsZ levels and FtsZ structure in sfiD+ and sfiD strains. In other experiments, the secondary "cold sensitive" phenotype of the mutants will be exploited. Cold resistant revertants will be selected and analyzed for "second site" mutations which can identify genes whose products interact with the SfiD product. Further physiological characterization of the mutants will include analysis of division rates, cell size and pattern of nucleoid distribution. Finally, a structural analysis of the sfiD region, including molecular cloning, transposon mutagenesis and protein identification, will be initiated.